Synthesis gas, which is also known as syngas, is a mixture of gases comprising carbon monoxide (CO) and hydrogen (H2). Generally, syngas may be produced from any carbonaceous material. In particular, biomass such as agricultural wastes, forest products, grasses, and other cellulosic material may be converted to syngas.
Syngas is a platform intermediate in the chemical and biorefining industries and has a vast number of uses. Syngas can be converted into alkanes, olefins, oxygenates, and alcohols such as ethanol. These chemicals can be blended into, or used directly as, diesel fuel, gasoline, and other liquid fuels. Syngas can also be directly combusted to produce heat and power. The substitution of alcohols and/or derivatives of alcohols in place of petroleum-based fuels and fuel additives can be particularly environmentally friendly when the alcohols are produced from feed materials other than fossil fuels.
In recent years, considerable research has been devoted to providing alternative sources and manufacturing routes for liquid hydrocarbon fuels in recognition of the fact that petroleum is a non-renewable resource and that petroleum-based fuels such as gasoline and distillate will ultimately become more expensive.
Ethanol is a commercially viable liquid transportation biofuel today. Catalytic approaches for converting syngas to ethanol typically convert syngas to methanol which is then converted to ethanol and other alcohols. One of the most significant economic challenges to date has been the poor carbon selectivities to ethanol.
Other challenges in catalytically converting syngas into ethanol include the cost and availability of suitable catalysts, catalyst sensitivity to small amounts of sulfur and nitrogen, requirements for relatively high H2/CO feed ratios, and the generation of low-value co-products.
It is known that methanol can be converted into dimethyl ether (DME). Alternatively, syngas can be converted directly into DME by mixed catalysts with activities for generating methanol from syngas and for dehydrating methanol to DME. The DME can be carbonylated to produce methyl acetate, which can be hydrogenated to produce methanol and ethanol. The methanol can be recycled so that ethanol is the primary product. While this process is generally disclosed in the art, there remains a need for new process variations that allow for better overall economics—including capital-cost reduction, reduced process complexity, operating flexibility, and co-product potential.
What are desired, in view of the art and various commercial issues, are improved process configurations and apparatus for conversion of syngas (e.g., from biomass) and/or methanol into ethanol through DME as an intermediate.